1. Field of the Invention
The present invention relates to an ink composition, and more particularly to an ink composition suitable for ink jet recording.
2. Background Art
Use of a solvent for dissolving or dispersing a colorant is indispensable to recording methods using an ink composition. A mixed solvent composed of water and a water-soluble organic solvent has been extensively used as the solvent component from the viewpoint of safety. Upon application of an ink composition on a recording medium, the solvent penetrates the recording medium or evaporates to permit the colorant to be fixed onto the recording medium, thereby recording letters or other images on the recording medium. Various properties are required of the formed images.
Regarding lightfastness among the property requirements, various proposals have been made in the art to improve this property. Water-soluble dyes, by virtue of good water solubility, have been extensively used as a colorant for water-base ink compositions. However, it has been pointed out that the water-soluble dyes generally have poor lightfastness. In order to solve this problem, an ink composition with a colorant, not soluble in water, having excellent lightfastness, such as a pigment, being dispersed therein has been proposed in the art.
However, it has been pointed out that, although inorganic pigments, such as carbon black, and metal-containing organic pigments, such as copper phthalocyanine pigment, are excellent in lightfastness, most of the other organic pigments cannot produce an image having satisfactory lightfastness. Therefore, improving the lightfastness of the ink composition using an organic pigment as the colorant has been required in the art.
On the other hand, dyes are attractive in that the number of kinds of dyes usable in the Ink composition is large. Therefore, also in the case of the ink composition comprising a dye as the colorant, improving the lightfastness of the printed image has been desired in the art.
In recent years, formation of a color image using a plurality of ink compositions has been carried out. In the color image using the plurality of ink compositions, the presence of only one color having poor lightfastness leads to a change in hue of the image and consequently extremely deteriorates the quality of the color image. Thus, more controlled lightfastness is required of color ink compositions.
Further, in recent years, ink jet recording printers have become widely spread. Ink jet recording is a printing method wherein droplets of an ink composition are ejected and deposited onto a recording medium such as paper to conduct printing. This printing method is advantageous in that a high-resolution, high-quality image can be printed at a high speed using a relatively inexpensive apparatus. In particular, a color ink jet recording apparatus can provide an improved image quality and has become used as an output device for photographs and also as a digital printer, a plotter, a CAD output device and the like. Images printed by the ink jet recording printer which has become widely used in the art are considered to be utilized in various forms. In particular, photograph-like prints are considered to be put for display in a place exposed to light from a fluorescent lamp or direct sunlight in the open for a long period of time. Therefore, lightfastness is a very important property requirement to be satisfied by the ink composition used in the ink jet recording.
Addition of an ultraviolet absorber or a light stabilizer to the ink composition is considered effective for improving the lightfastness of the ink composition. Since, however, most of the ultraviolet absorbers and the light stabilizers are oil soluble, incorporation thereof in a satisfactory amount in the water-soluble ink composition is difficult.
On the other hand, a new ink jet recording method has been recently proposed which comprises applying a polyvalent metal salt solution onto a recording medium and then applying an ink composition containing a dye material having at least one carboxyl group (for example, Japanese Patent Laid-Open No. 202328/1993). According to this method, polyvalent metal ions combine with the dye to form an insoluble composite which can provide a high-quality image having waterfastness and free from color bleeding.
Further, an ink jet recording method has been proposed wherein a color ink containing at least a surfactant or a penetrable solvent and a salt for imparting a penetrating property is used in combination with a black ink which cooperates with the salt to cause thickening or agglomeration, thereby providing a high-quality color image having high image density and free from color bleeding (Japanese Patent Laid-Open No. 106735/1994). More specifically, in this method, two liquids, i.e., a first liquid containing a salt and a second liquid of an ink composition, are printed to provide a good image.
Furthermore, other ink jet recording methods wherein two liquids are printed have been proposed, for example, in Japanese Patent Laid-Open No. 240557/1991 and No. 240558/1991.
The present inventors now propose a technique for improving the lightfastness of an ink composition wherein a polymer having an ultraviolet absorbing capacity and/or a light stabilizing capability and, in addition, a film-forming property are added as a fine particle to the ink composition.
Accordingly, an object of the present invention is to provide an ink composition which can realize a printed image having excellent lightfastness.
More specifically, the present invention aims to provide an ink composition which can produce an image excellent in lightfastness as well as in rubbing/scratch resistance and waterfastness and, in addition, having an excellent print quality free from feathering or color bleeding.
Another object of the present invention is to provide an ink composition which can be highly stably ejected in ink jet recording and in addition possesses excellent storage stability.
A further object of the present invention is to provide an ink composition which, when used in a recording method using the so-called xe2x80x9ctwo liquids,xe2x80x9d can yield an image having good quality, especially an image free from feathering and color bleeding.
According to the present invention, there is provided an ink composition comprising a colorant, water, a water-soluble organic solvent, and a fine particle of a polymer, the fine particle comprising a polymer having a film-forming property, an ultraviolet absorbing capacity and/or a light stabilizing capability.